The present invention relates to an apparatus and method for charging combustible solids into rotary kilns. More particularly, the present invention provides an apparatus and integrated firing system for providing smoother firing of kilns and for controlling firing parameters of interest, including both combustion driven parameters and regulatory driven parameters.
Cement kilns have received favorable review from both federal and state environmental regulatory agencies for disposal of both liquid and solid combustible waste materials. Cement kilns provide a combination of high operating temperatures and long residence times, both of which are favorable conditions for complete combustion of organic components of waste and chemical combination of inorganic components with the reactive in-process mineral components. Combustible waste solids provide a source of inexpensive energy for the mineral process in industry.
For many years, regulation compliant use and disposal of waste in operating kilns was limited to combustible liquid or "pumpable" hazardous waste. Liquid waste materials are easily blended with each other and with conventional fuels to provide homogeneous liquids that can be burned in the gaseous phase at the firing end of the kiln with little or no modification of kiln burner configuration. Solid waste, however, can occur in multiplicity of forms, from hard crystalline solids to viscous, sticky sludges. They are not easily blended, and they present significant engineering challenges for their safe handling and delivery into rotating kilns. Several apparatus have been designed to facilitate firing of solid wastes into kilns. U.S. Pat. No. 4,850,290, issued Jul. 25, 1989, incorporated herein by reference, describes an apparatus and method for delivering containerized waste to both pre-heater type and conventional long wet or dry kilns at the point in the process where the kiln gas temperature is such that volatized components are consumed with high destruction and removal efficiency. The '290 patent describes a device for delivering containerized waste through the wall of a kiln cylinder during kiln operation. The apparatus comprises a port, preferably with a mechanical closure, formed in the kiln cylinder wall. The port is aligned with a drop tube inside the kiln cylinder. The drop tube prevents hot mineral material in the kiln from escaping through the port or contacting closure. The device is utilized to deliver containerized waste into the kiln at predetermined time during kiln cylinder rotation.
Other apparatus and methods for delivering solid fuels, especially solid waste fuels, are known in the art. See, for example, U.S. Pat. No. 5,078,594, incorporated herein by reference, which discloses a charging apparatus for delivering tires or other combustible waste solids through a port into a rotating kiln.
One object of this present invention is to provide improved firing system for controlling both combustion driven parameters and regulatory driven parameters of dimensioned fuel modules charged into rotary kilns.
Another object of this present invention is to provide an automated system for smoother firing of the kilns, thereby simplifying a kiln operator's tasks.
Yet another object of this present invention is to increase capacity capabilities for firing solid waste derived fuel in the kilns.
Still another object of this present invention is to provide an apparatus and method capable of charging solid waste into a kiln at a variable rate when the kiln is rotating at a fixed rate.
Those and other objects of this invention are accomplished by providing a firing system and apparatus which controls the delivery of solid waste to kilns. The firing system of the present invention includes a staging assembly having a plurality of staging conveyors coupled to a main transfer assembly for transferring containers to the kiln. The contents of each container are sampled and coded with appropriate parameter information necessary to control the input of various parameters into the kiln. The kiln firing mechanism is concerned only with the primary combustion driven firing parameters. The primary or priority parameters for controlling kiln firing are heat energy (BTUs) and weight.
Secondary parameters for controlled kiln firing can be tailored to regulatory and/or combustion driven parameter requirements as needed. The present invention produces the most homogeneous and "hold point averaged" parameter of interest that is possible. In other words, the control system of the present invention operates to maintain selected parameters of interest as close as possible to a specified hold point parameter amount. Any parameter which the operator desires to control can be controlled by the system of the present invention. An example of some combustion driven parameters include heat energy or BTUs, weight, chloride content, volatility, particle size, iron content, and total inorganic residue content. Examples of regulatory driven parameters include the amount of cadmium, lead, arsenic, chromium, barium, or mercury contained in the solid waste charged with the kiln. These parameters remain indigenous to the geographic location, fuel supplier and regulatory climate.
Palletized loads of fuel modules or containers containing solid waste derived fuel are delivered from processors to the kiln site. Solid waste material in each of the containers is sampled to determine the amount of the parameter or element of interest in each of the containers. The containers are then labeled using an adhesive-backed bar code label indicating the quantity of the parameters of interest in the container. Coded containers are loaded onto an input conveyor and transported toward a staging assembly including a series of staging conveyors. A bar code reader reads the parameter information on each container and loads each container onto an appropriate staging conveyor based upon the parameter information. The parameter value is stored in a register of a computer memory for access during charging of the containers into the kiln. A computer is used to control delivery of the containers from the input conveyor to the appropriate staging conveyor by sending signals to open and close appropriate gates on staging conveyors. Containers on each staging conveyor are accumulated until the containers are required upon demand from the firing system.
The computer controlled firing system automatically calculates the most correct combination of containers having high and low parameter values to approximate a desired hold point of the parameter value. The computer controls gates to open and close the staging assembly conveyors to load containers onto a transfer conveyor in an appropriate sequence. Containers moving on the transfer conveyor pass over a scale capable of weighing the containers on the fly and indicating the instantaneous feed rate and cumulative feed rate to the central control. The cumulative feed rate is printed out at the end of a shift as total weight and total number of containers.
Each container is presented to a charging apparatus assembly only at an appropriate time commensurate with the hold point firing range as set in central control and with an inhibit/non-inhibit signal provided by a kiln exit gas monitoring system. This signal is controlled by trigger levels preset to limits required by the gas emissions permit and automatically discontinues firing of the system when the outputs exceed regulatory limits.
The fuel flow rate to the kiln is variable in a step-wise manner and is controllable by presentation of the fuel to automatic pick-up tubes designed as an integral part of the charging apparatus. By providing a plurality of pick-up tubes, and by controlling the time at which containers are presented to selected pick-up tubes, it is possible to provide a variable input rate for containers into a kiln having a fixed rotation rate. The firing system also controls opening and closing of the port in each tube by controlling operation of a valve. The valve remains closed until it is time to drop the solid waste into the kiln to prevent the undesirable flow of ambient air into the kiln via the tubes. The computer control generates a signal to open the valve at the precise moment to drop the containers into the kiln and closes the valve after the fuel has been charged to the kiln. Charging of the kiln is verified by an infrared sensor which senses the absence of the fuel in the entry tube.
According to one aspect of the present invention, an apparatus is provided for charging combustible fuel modules into a heated zone of a rotating kiln cylinder. The apparatus includes a generally cylindrical outer wall configured to replace a section of the rotating kiln cylinder. The cylindrical outer wall is formed to include at least two ports therein. The ports are spaced apart along a periphery of the outer wall. The apparatus also includes means for charging fuel modules into the kiln through the at least two radially spaced apart ports formed in the outer wall so that more than one fuel module can be charged into the kiln cylinder at radially spaced apart locations during each revolution at the kiln cylinder. The charging means is coupled to the outer wall.
In the illustrated embodiment, the charging means includes at least two drop tubes, one drop tube extending through each of the ports and into the heated zone of the rotating kiln cylinder so that fuel modules can be charged into the rotating kiln cylinder through the drop tubes at radially spaced apart locations of the kiln cylinder.
Also in the illustrated embodiment, the apparatus further includes a closure for each port. Each closure is movable between a port-closed position and a port-opened position. The apparatus also includes means for moving each closure selectively between the port-closed position and the port-opened position to charge modules through the selected port and into the heated zone.
The apparatus still further includes a staging assembly for supporting fuel modules, and means for transferring a fuel module between the staging assembly and a selected one of the drop tubes to charge the fuel module into the kiln cylinder through the port in communication with the selected drop tube. The transferring means includes at least two transfer tubes, one transfer tube being coupled to each drop tube and means for selectively transferring fuel modules from the staging assembly into a selected transfer tube to charge the fuel module into the kiln cylinder through the drop tube aligned with the selected transfer tube. The means for selectively transferring fuel modules from the staging assembly into a selected transfer tube includes an elevator assembly for lifting fuel modules upwardly from the staging assembly into alignment with the selected transfer tube as the kiln cylinder rotates.
The illustrated embodiment further discloses a charging apparatus including a first set of drop tubes aligned at a first axial position along the longitudinal axis of the generally cylindrical outer wall, and a second set of drop tubes aligned at a second axial position along the longitudinal axis of the generally cylindrical outer wall spaced apart from the first axial position. The apparatus also includes first means for transferring a fuel module into a selected drop tube in the first set of drop tubes, and second means for transferring a fuel module into a selected drop tube in the second set of drop tubes.
The first and second transferring means each include an elevator for lifting fuel modules upwardly from the staging assembly into alignment with the first and second sets of drop tubes, respectively. The elevators each include a pair of spaced-apart, parallel plates for engaging a bottom surface of each fuel module, and means for moving the parallel plates relative to the staging assembly to lift the fuel module away from the staging assembly.
According to another aspect of the present invention, a firing system is provided for charging a plurality of incoming combustible fuel modules containing a known amount of a parameter of interest into a heated zone of a rotating kiln. The firing system includes means for separating incoming fuel modules into a plurality of stages based on the parameter amount in each fuel module, and means for removing fuel modules from the plurality of stages in a selected order to maintain an average parameter amount for fuel modules charged into the kiln at substantially a preselected level. The firing system also includes means for charging fuel modules into the kiln in the selected order.
In the illustrated embodiment of the invention, incoming fuel modules are transported to the firing system on an inlet conveyor. The separating means includes a plurality of staging conveyors and means for deflecting each incoming fuel module from the inlet conveyor onto a selected staging conveyor based on the parameter amount in each fuel module.
The charging means includes a transfer conveyor for moving fuel modules from the plurality of staging conveyors toward the kiln and means for transferring fuel modules from the transfer conveyor into the kiln. The means for removing fuel modules from the plurality of stages includes a plurality of gates for blocking movement of fuel modules from the plurality of staging conveyors onto the transfer conveyor and means for selectively opening the gates to permit movement of fuel modules from the plurality of staging conveyors onto the transfer conveyor in the selected order. The means for selectively opening the plurality of gates includes means for determining which of the next available fuel modules in each of the plurality of stages will provide an optimum parameter value to maintain the average value of the parameter of interest supplied to the kiln at substantially the preselected level.
According to yet another aspect of the present invention, an apparatus is provided for charging a plurality of combustible solid waste fuel modules containing a known amount of a parameter of interest into a heated zone of a rotating kiln. The apparatus includes means for determining an optimum time to charge each fuel module into the rotating kiln to maintain the average value of the parameter of interest supplied to the kiln substantially at a preselected level, and means for charging each fuel module into the kiln at substantially said optimum time.
In the illustrated embodiment, the apparatus also includes means for storing the amount of the parameter of interest by weight of each fuel module, and means for weighing each fuel module. The apparatus further includes means for calculating the amount of the parameter of interest in each fuel module using the stored amount of the parameter of interest in each fuel module and the measured weight of each fuel module.
The determining means includes means for calculating an optimum firing interval for a next available fuel module based upon an average parameter value of fuel modules previously charged into the kiln and the parameter value of the next available fuel module. The firing interval is selected to maintain the average parameter value at substantially said preselected level.
According to still another aspect of the invention, a method is provided for charging a plurality of incoming fuel modules containing combustible material into a heated zone of a rotating kiln. The method includes the steps of separating the incoming fuel modules into a plurality of different stages based upon the amount of the parameter contained within each fuel module, and removing fuel modules stored in the plurality of stages in a selected order to maintain an average amount of the parameter charged into the kiln at substantially a preselected level. The method also includes the step of charging the selected modules into the kiln in the selected order.
In the illustrated method, the removing step includes the steps of calculating which of the next available fuel modules from the plurality of stages provides an optimum parameter amount to maintain the average parameter amount at substantially said preselected level, and transferring the next available fuel module from the stage which provides the optimum parameter amount computed during the calculating step to the kiln for the charging step.
The method further includes the steps of sampling the combustible material in each of the plurality of fuel modules to determine an amount of a parameter of interest within each fuel module, and labeling the fuel modules to indicate the amount of the parameter within each fuel module. The method still further includes the step of storing the amount of the parameter in each fuel module in a computer memory.
The method also includes the steps of determining an optimum time to charge each fuel module into the rotating kiln to maintain the average value of the parameter of interest supplied to the kiln substantially at a preselected level. Each fuel module being charged into the kiln at substantially said optimum time during the charging step.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.